The actual design and implementation of your data model and application are going to be far more important for performance. My suggestion would be to start on M

The actual design and implementation of your data model and application are going to be far more important for performance. My suggestion would be to start on MySQL and migrate to another platform if it becomes necessary. You also have to ask what kind of skill sets do you have around and what are you likely to have in the future. A well configured and maintained installation of either platform will out peform a bad one. So are you windows geeks or linux geeks?